1. Field of the Invention
The invention relates to novel medicinal substances which selectively control tumor tissue, while healthy tissue is virtually not attacked. The novel medicinal substances are therefore outstandingly suitable for cancer therapy.
2. Background Art
Prior art medicines used in chemotherapy are, as a rule, only partly successful, i.e. they do not result in a definitive cure. In addition, the substances used in the prior art frequently act only on a particular category of tumors. Another disadvantage of the chemotherapeutic agents currently known are their frequently harmful side effects, because chemotherapeutic agents are generally able to have cytostatic effects on proliferating tissue. The known chemotherapeutic agents are also unsatisfactory in controlling metastasis formation, and this is one of the main reasons which has prevented decisive success in cancer therapy to date.
It is known that tumor tissue has, in the extracellular media, a reduced average pH of about 6.5 to 7.0, and the pH on the surface of cancer cells may even fall to 5, whereas the pH in normal tissue and in blood is about 7.2 to 7.5, and this is described, for example, in DE-A 44 07 484 and in Tumor Biol., 1994, 15: 304-310. These publications disclose that the natural immune defenses are blocked by the reduction in the pH range in tumor cells, because the body's own defense cells react with full cytotoxicity for cancer target cells only in the slightly basic media of more than 7. DE-A 44 07 484 therefore proposes bringing the acidic external media of cancer cells to the normal physiological pH level of 7 to 7.5 and thus controlling the cancer cells by the body's own immune defenses. To this end, the acidic external media of cancer cells is brought to a physiological pH of 7 to 7.5 either by artificial alkalinization measures or by preventing the acidification process itself.
Although the medicinal products described in DE-A 44 07 484 represent an advance in cancer therapy, it would be desirable to have available medicinal products which, besides the body's own immune defenses, selectively control tumor cells and thus can be used as chemotherapeutic agents with relatively few side effects.